Conventionally, there has been an eddy current brake which performs braking by electromagnetic induction using a three-phase alternating current, as described in the Unexamined Japanese Patent Publication No. 61-266064. As shown in FIG. 6, such an eddy current brake 100 comprises a brake disc 102 attached to an axle 106 so that a disc surface 104 is perpendicular to the axle 106, and a stator 108 which is provided in a position facing the disc surface 104 and which, when excited, generates a moving magnetic field which moves to a direction opposite to a rotation direction of the brake disc 102. The eddy current brake 100 moves the moving magnetic field so that the slip reaches one (1) or more, as shown in FIG. 7. When this moving field excited by the stator 108 generates an eddy current on the disc surface 104, a force operating to a direction opposite to the rotation direction of the brake disc 102 is applied to the brake disc 102 according to the Fleming's left-hand rule, and thus, braking is performed using the force.
In the eddy current brake 100, almost all the kinetic energy of a wheel 110 is converted into heat energy by the eddy current passing on the brake disc 102, and consequently the brake disc 102 becomes hot. However, it is clearly not structurally preferable that a temperature of the brake disc 102 becomes high exceeding a certain temperature. Therefore, in the conventional eddy current brake 100, the brake disc 102 is made thick to increase heat capacity and to facilitate heat radiation. Also, a cooling device such as a fan is provided to cool the brake disc 102 forcibly so as to prevent the brake disc 102 from getting too hot exceeding the certain temperature.
On the other hand, to speed up a railway car of a bullet train, etc., it is necessary to reduce the weight of the car and to enhance the braking force
However, the conventional eddy current brake 100 requires thicker brake disc 102 to increase heat capacity, etc. and a fan to be provided to enhance the braking force, thereby resulting in increase in weight.